The Supreme Court heard oral arguments yesterday over a Los Angeles County prosecutor's allegation that he was punished for speaking truth to power in a case that could affect the at-work free-speech rights of the country's 20 million public employees.

Richard Ceballos said he was demoted and mistreated by supervisors after he wrote a memorandum accusing sheriff's deputies of lying to get a search warrant, and then testified in favor of the defendant in the case at a court hearing.

He sued then-District Attorney Gil Garcetti, the county government and others in federal court in October 2000, saying that this alleged retaliation was a violation of his First Amendment right to speak out on matters of public importance. A district judge dismissed his suit, but last year the U.S. Court of Appeals for the 9th Circuit, based in San Francisco, said it could proceed. The Los Angeles officials and the county government appealed to the Supreme Court.

They argued that the 9th Circuit ruling would turn every disgruntled public employee into a free-speech plaintiff in federal court. "This case is about whether a public employee has a constitutional right to do his job in a way that is not to the satisfaction of his employer," their lawyer, Cindy S. Lee, told the justices yesterday. There is no such right, she argued.

The Bush administration supports the defendants in the case. And yesterday several justices seemed to sympathize with their point of view. Justice Anthony M. Kennedy, normally a proponent of broad free-speech protections, told Ceballos's lawyer, Bonnie I. Robin-Vergeer, that the First Amendment "isn't about policing the workplace."

But she said the recent troubles at the Federal Emergency Management Agency show that it is "critically important" to protect civil servants who speak out against the mistakes of their supervisors.

Ceballos is supported by, among others, the National Education Association, the National Treasury Employees Union and the American Civil Liberties Union.

In a past case, the court gave public employees protection for statements they made on matters of "public concern" outside of work. In another case, it denied protection to an internal workplace communication that was not about public matters. The precedents ask the lower courts to balance an employee's free-speech interests against the employer's interest in workplace discipline.

But this case poses the issue of internal comment on a matter of public concern: Police misconduct was a hot issue in Los Angeles at the time of Ceballos's allegation because of a local scandal, which involved allegations of massive police perjury.

Though the court seemed generally skeptical about extending the First Amendment's protections to situations such as Ceballos's, some justices were hesitant to rule out that possibility. Justice Stephen G. Breyer suggested that the answer might be to prohibit "unreasonable" discipline for on-the-job statements, asking, "Can't we limit [the supervisor's] discretion?"

The case is Garcetti v. Ceballos, No. 04-473. A decision is expected by July.